1. Field of the Invention
This invention relates to color changing compositions and devices that visually monitor a sterilization cycle.
2. Description of the Prior Art
Devices that contain chemical compositions that will change color when exposed to alkylating sterilants, such as ethylene oxide, under sterilization conditions are known as sterilization indicators. They are one means of monitoring the effectiveness of a sterilization process such as those cycles used in hospitals for sterilizing glassware, medical instruments and wrapped goods. Indicators are placed within the sterilization chamber inside or with the goods to be sterilized (load).
Color changes occur because of the reaction between the chemical ingredients in the indicator and the alkylating sterilant (i.e. ethylene oxide). The indicator is further designed so that the reaction will take place at the particular ethylene oxide concentration, moisture and temperature, that is required to achieve sterility in the load. It may also be adjusted to the time period of the particular sterilization cycle if this is desired.
It is therefore not adequate for an indicator just to change color when exposed to ethylene oxide; it must respond in an integrated manner to all of the parameters encountered in a sterilization cycle, specifically time, temperature, pressure, humidity and concentration of sterilant.
A popular means of monitoring ethylene oxide sterilization relies on detecting visually a pH change within an indicator; the pH changes are produced when ethylene oxide reacts with the specified chemical of the indicator in the presence of a pH sensitive dyestuff.
Other means of monitoring ethylene oxide sterilization depend on alkylation of a specified chemical by ethylene oxide to produce a color compound.
Some of the known chemicals utilized in indicators are substituted pyridines and isoquinolines, halide salts of metals, magnesium chloride, 4,4'(nitro-benzyl)pyridine, and triphenylmethanes.
Problems associated with prior indicators include:
(1) Weak or ambiguous color changes, PA1 (2) Use of heavy metal salts or other toxic ingredients, PA1 (3) Measuring an induced change, such as pH rather than a direct sterilization effect of ethylene oxide.
and
Triphenylmethane dyes are part of a large, well-known group of commercially available organic synthetic dyes called the triarylmethane dyes. Triarylmethane dyes are derivatives of triphenylmethane (C.sub.6 H.sub.5).sub.3 CH and diphenylnaphthylmethane (C.sub.6 H.sub.5).sub.2 CH(C.sub.10 H.sub.7) to which auxochromic and bathochromic (color producing) groups like amino (NH.sub.2) and hydroxyl (OH) have been added. A triarylmethane dye is formed in substantially the following stages: formation of a colorless leuco base; conversion of the leuco base to the colorless carbinol or color base, and finally formation of the triarylmethane dye (which is a resonance hybrid radical-ion) by treatment (oxidation) with acid.
In the aldehyde method of preparation of triarylmethane dyes, an aromatic aldehyde provides the central carbon atom of the dye radical. Two moles of an aromatic amine are condensed with an aromatic aldehyde to yield the leuco base. The leuco base is oxidized to the carbinol base, which, in the presence of acid, is converted to the dye.
In a hydrol synthesis, the central carbon atom is supplied by a substituted benzhydrol, such as Michler's hydrol.
Thus a leuco base form and Michler's hydrol (which is termed an intermediate in a dye synthesis) are precursors in the formation of triarylmethane dyes. With the exception of the leuco base, crystal violet lactone, which has been used in the production of a new kind of carbonless copy paper, these precursors have not obtained end uses.